1. Field of the Invention
This disclosure relates in general to magnetic storage systems, and more particularly to a method and apparatus for providing diamagnetic flux focusing in a storage device.
2. Description of Related Art
There has been huge progress in the field of magnetic storage system technology in almost 50 years. Moreover, the rate of this progress is increasing year after year. Such success has made storage systems an important component of modern computers.
Some of the most important customer attributes of any storage system are the cost per megabyte, data rate, and access time. In order to obtain the relatively low cost of today's storage system compared to solid state memory, the customer must accept the less desirable features of this technology, which include a relatively slow response, high power consumption, noise, and the poorer reliability attributes associated with any mechanical system. On the other hand, magnetic storage systems have always been nonvolatile; i.e., no power is required to preserve the data, an attribute which in semiconductor devices often requires compromises in processing complexity, power-supply requirements, writing data rate, or cost.
Improvements in areal density have been the chief driving force behind the historic improvement in storage cost. In fact, the areal density of magnetic storage systems continues to increase. While nature allows us to scale down the size of each bit of information, it does not allow scaling to happen forever.
Today, as the magnetic particles that make up recorded data on a storage system become ever smaller, technical difficulties in writing and reading such small bits occur. Further, as areal density increases, the requirements put on head designs will change.
In a magnetic head, a read element and a write element are formed having an air bearing surface ABS, in a plane, which can be aligned to face the surface of the magnetic disk. The read element includes a first shield, a second shield, and a read sensor that is located within a dielectric medium between the first shield and the second shield. The most common type of read sensor used in the read/write head is the magnetoresistive (AMR or GMR) sensor, which is used to detect magnetic field signal changes in a magnetic medium by means of changes in the resistance of the read sensor imparted from the changing magnitude and direction of the magnetic field being sensed.
The write element is typically an inductive write element that includes the second shield that functions as a first pole for the write element and a second pole disposed above the first pole. The first pole and the second pole contact one another at a backgap portion, with these three elements collectively forming the yoke. The combination of a first pole tip portion and a second pole tip portion near the ABS are sometimes referred to as the ABS end of the write element. Some write elements have included a pedestal that can be used to help define track width and throat height. A write gap is formed between the first and second poles in the area opposite the back gap portion. The write gap is typically filled with a non-magnetic, electrically insulating material that forms a write gap material layer. A conductive coil passes through the yoke. The write head operates by passing a writing current through the conductive coil. Because of the magnetic properties of the yoke, a magnetic flux is induced in the first and second poles by write currents passed through the coil. The write gap allows the magnetic flux to fringe out from the yoke thus forming a fringing gap field and to cross the magnetic recording medium that is placed near the ABS.
Areal density, also sometimes called bit density, refers to the amount of data that can be stored in a given amount of hard disk platter “real estate”. Since disk platters surfaces are of course two-dimensional, areal density is a measure of the number of bits that can be stored in a unit of area. It is usually expressed in bits per square inch (BPSI).
Being a two-dimensional measure, areal density is computed as the product of two other one-dimensional density measures: track density and linear recording density. Track density is a measure of how tightly the concentric tracks on the disk are packed, i.e., how many tracks can be placed down in inch of radius on the platters. Linear recording density is a measure of how tightly the bits are packed within a length of track.
Presently available write poles lack the ability to generate localized magnetic recording fields with the density required for future areal density goals. Smaller, more localized magnetic recording fields are important for minimizing the trackwidth. Narrowing of the recording track causes the recording magnetic field to leak. In order to prevent this leakage magnetic field from generation, in the conventional magnetic head, track end surfaces (side surfaces) of the magnetic poles are trimmed. However, even using this trimming method, the leakage magnetic field cannot be sufficiently suppressed at the track ends of the magnetic head but some magnetic field leaks through a recording gap layer made of non-magnetic insulating material.
One approach has been to form a non-magnetic conductive material member in contact with at least a part of the respective side surfaces of the upper magnetic pole layer and in contact with the lower magnetic pole layer. The eddy current flows not only within the magnetic poles as in the conventional magnetic head but also through the non-magnetic conductive material members that are formed in contact with the track end surfaces of the upper magnetic pole. Therefore, the leakage flux is reduced somewhat to increase the magnetic field passing through the recording gap layer. The non-magnetic material used was Cu, Al, Au or alloys thereof. However, these materials do not sufficiently focus the magnetic flux within the write gap.
It can be seen then that there is a need for a method and apparatus for providing improved flux focusing in a write head.